In the field of telecommunications, it is sometimes necessary to combine together radiofrequency signals deriving from different sources, for example in order to retransmit them to a same recipient, or simply by means of a same antenna. It may be that the spectra of these signals partly or totally overlap; in this case, it is necessary to proceed with frequency conversions to prevent these signals from interfering with one another. Furthermore, frequency conversions may be made necessary, for example, in order to retransmit over a downlink signals received via an uplink. Each frequency conversion operation entails the use of a distinct radiofrequency mixer, driven by a local oscillator. When there are a large number of signals to be handled, that can lead to the implementation of cross-connect and frequency conversion devices that are very complex, and therefore expensive, heavy, bulky and consumers of power (these last three parameters being particularly detrimental in space applications).
FIG. 1 schematically illustrates the structure and the operation of a cross-connect and frequency conversion device according to the prior art DEIC. The device has twelve inputs PE1-PE12 (the number 12 is given purely by way of example) for respective radiofrequency signals RFin1-RFin12, collectively designated by the reference RFin. These signals, that are assumed to all have the same frequency fs, or in any case spectra that at least partially overlap, are supplied as input to respective radiofrequency mixers, MRF1-MRF12, which also receive, on another input, radiofrequency signals generated by local oscillators OL1-OL3, operating at different (radio)frequencies, fOL1, fOL2, fOL3. More specifically, the mixers MRF1, MRF2, MRF3 and MRF4 receive, on a first input, the signals RFin1, RFin2, RFin3, RFin4, respectively, and, on a second input, a same signal generated by the local oscillator OL1; the mixers MRF5, MRF6, MRF7 and MRF8 receive, on a first input, the signals RFin5, RFin6, RFin7, RFin8, respectively, and, on a second input, a same signal generated by the local oscillator OL2; and the mixers MRF9, MRF10, MRF11 and MRF12 receive, on a first input, the signals RFin9, RFin10, RFin11, RFin12, respectively, and, on a second input, a same signal generated by the local oscillator OL3.
As is known per se, the signals at the output of the mixers MRF1-MRF4 have a component at a frequency fs+fOL1 and another component at a frequency fs-fOL1; similarly, the signals at the output of the mixers MRF5-MRF8 have components at the frequencies fs±fOL2 and those at the output of the mixers MRF9-MRF12 at the frequencies fs±fOL3.
Four multiplexers MUX1, MUX2 MUX3 are then provided to combine three signals deriving from each of the three groups of mixers (MRF1-MRF4), (MRF5-MRF8), (MRF9-MRF12). These multiplexers are moreover equipped with filters making it possible to reject the spectral components at the difference frequency (fs−fOLi, i=1, 2 or 3) and retain only those at the sum frequency (fs+fOLi, i=1, 2 or 3), or vice-versa.
On the output ports PO1, PO2, PO3, PO4 of the multiplexers (and of the device DEIC) there are four “composite” radiofrequency signals RFout1, RFout2, RFout3, RFout4, each consisting of the juxtaposition of three “elementary” signals obtained by frequency-shifting of three respective input signals. Thus, the output signal RFout1 groups together (with frequency shift) the signals RFin1, RFin5 and RFin9; the output signal RFout2 groups together RFin2, RFin6, RFin10; the output signal RFout3 groups together RFin3, RFin7, RFin11; and the output signal RFout4 groups together RFin4, RFin8, RFin12. The reference symbols 1 to 12 make it possible to associate the input signals with the corresponding composite output signals.
The main drawback with the device DEIC is that, to process N radiofrequency signals, N mixers are required, which can rapidly lead to an unacceptable complexity.
The invention aims to remedy this drawback.